linux-kernel - Re: [RFC] hotplug, memory: move register_memory_resource out of the lock_memory

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Date:	Wed, 15 Jan 2014 10:12:46 +0900
From:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
To:	Nathan Zimmer <nzimmer@....com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Tang Chen <tangchen@...fujitsu.com>,
	Wen Congyang <wency@...fujitsu.com>,
	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Hedi <hedi@....com>, Mike Travis <travis@....com>,
	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] hotplug, memory: move register_memory_resource out of the
 lock_memory_hotplug

(2014/01/15 3:24), Nathan Zimmer wrote:
> We don't need to do register_memory_resource() since it has its own lock and
> doesn't make any callbacks.
> 
> Also register_memory_resource return NULL on failure so we don't have anything
> to cleanup at this point.
> 
> 
> The reason for this rfc is I was doing some experiments with hotplugging of
> memory on some of our larger systems.  While it seems to work, it can be quite
> slow.  With some preliminary digging I found that lock_memory_hotplug is
> clearly ripe for breakup.
> 
> It could be broken up per nid or something but it also covers the
> online_page_callback.  The online_page_callback shouldn't be very hard to break
> out.
> 
> Also there is the issue of various structures(wmarks come to mind) that are
> only updated under the lock_memory_hotplug that would need to be dealt with.
> 
> 
> cc: Andrew Morton <akpm@...ux-foundation.org>
> cc: Tang Chen <tangchen@...fujitsu.com>
> cc: Wen Congyang <wency@...fujitsu.com>
> cc: Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> cc: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
> cc: "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
> cc: Hedi <hedi@....com>
> cc: Mike Travis <travis@....com>
> cc: linux-mm@...ck.org
> cc: linux-kernel@...r.kernel.org
> 
> 
> ---

The patch seems good to me.

Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>

Thanks,
Yasuaki Ishimatsu

>   mm/memory_hotplug.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 1ad92b4..62a0cd1 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1097,17 +1097,18 @@ int __ref add_memory(int nid, u64 start, u64 size)
>   	struct resource *res;
>   	int ret;
>   
> -	lock_memory_hotplug();
> -
>   	res = register_memory_resource(start, size);
>   	ret = -EEXIST;
>   	if (!res)
> -		goto out;
> +		return ret;
>   
>   	{	/* Stupid hack to suppress address-never-null warning */
>   		void *p = NODE_DATA(nid);
>   		new_pgdat = !p;
>   	}
> +
> +	lock_memory_hotplug();
> +
>   	new_node = !node_online(nid);
>   	if (new_node) {
>   		pgdat = hotadd_new_pgdat(nid, start);
> 


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